[reportlab-users] Bug Report: Default parameter closure bug in several Graphics and Platypus classes

[Robin Becker]

Nate Silva wrote:

> SUMMARY

> 

> On this list yesterday I complained about, and Tim Roberts identified, a bug that causes Frames to be duplicated between PageTemplates.

> 

> See Tim Roberts' e-mail dated 30-Nov-2009 (US) / 01-Dec-2009 (EU).

> 

> Here is part of PageTemplate.__init__:

.........

> FINDINGS

> 

> The bug occurs anywhere an empty list [] default argument is assigned to an instance variable. These are in the latest Subversion (revision 3604):

> 

>    reportlab.graphics.shapes.Polygon (shapes.py:1208)

>    reportlab.graphics.shapes.PolyLine (shapes.py:1230)

>    reportlab.platypus.doctemplate.PageTemplate (doctemplate.py:246)

>    reportlab.platypus.flowables.KeepInFrame (flowables.py:878)

>    reportlab.platypus.flowables.FrameSplitter (flowables.py:1145)

>    reportlab.platypus.flowables.DocIf (flowables.py:1288)

> 

> SAMPLE CODE

> 

>........

> http://gist.github.com/246511

> 

> Regards,

> Nate

thanks for the report and search. This will be fixed today. These modules were 
coded a long time ago and probably I (or whoever coded them) wasn't really 
thinking hard enough about all the use cases.

I think I prefer to indicate the usage in the argument default so we'll probably 
use something like

     def __init__(.....,frames=[],....):
         ......

         self.frames = frames or []

which makes the actual value new each time.
-- 
Robin Becker